Papers by Author: Yong Kang Zhang

Abstract: Aluminum flyer with thickness of 50μm and diameter of 1mm had been driven successfully by high-power Nd:Glass laser system. Average speed of the flyer was detected by piezoelectric Polyvinylidene Fluoride (PVDF) transducer, which reached 6.67km/s. Extent of damage to protective materials of spacecrafts was studied after they were hit by the driven aluminum flyer. The protective materials of spacecraft were damaged structurally in our experiment, and the damage observed under the microscope was also shown. It could be seen that the flyer knocked a tiny hole with diameter of about 1mm in the protective cellular board, and there were traces of impact damage around the tiny hole, which indicated that protective materials of spacecrafts would be damaged structurally when they were hit by flyer with size of 1mm. At the same time, the hyperspeed flyer still had good integrity and flatness. The results showed that laser-shockwave-driven hyperspeed flyer technology could be used as an effective experiment means to simulate high-speed space particles, which made it feasible to establish a set of simulation device of laser-shockwave-driven hyperspeed flyer for the research of protective materials of spacecrafts on the ground.

Abstract: The purpose of this paper is to analyze the electromechanical properties of piezoelectric harvesting unit from road vibration. A new kind of piezoelectric harvesting unit, which consists of 8 pieces of PZT vibrators and sizes of 280*280*20mm, is purposed. The vibrators are connected and covered by epoxy resin. With the software of ANSYS, open circuit voltage and stress distribution of the unit under the function of vehicle tire pressure are analyzed. The results show that the maximums of open circuit voltage and stress distribution are proportional with the tire pressure. When the tire pressure is 1.0MPa, open circuit voltage and the maximum stress generated by the piezoelectric unit are 950.8V and 9.8MPa, respectively. It means that application of the piezoelectric harvesting unit can couple with the asphalt pavement very well and harvest higher electricity from road vibration on larger area.

Abstract: The 3-D numerical model of wave tank is developed considering the effects of wave generating and absorbing based on viscous fluid motion differential equations (N-S equation) and the volume of fluid (VOF) method by the use of FLUENT solver. The simulation is also made by the analysis of the existing methods of wave simulation. The wave form of the 3-D wave tank is analyzed with the result of diverse diversification at different wave location and their relationship. The flow path of each particle of the wave during the propagation is also been analyzed, which provides guidance for the wave form analysis.

Abstract: Fatigue tensile treatment was performed on 00Cr12 heat-resistant steel specimens which had been treated by laser shock processing (LSP). The unilateral tolerance factor statistical analysis method and the two-dimensional Weibull distribution method were used to predict the values of fatigue safe lives of the specimens respectively. The results indicate that the fatigue lives of 00Cr12 specimens were enhanced greatly after LSP, and improved by 62% compared with the specimens which were not treated by LSP. The unilateral tolerance factor method obtained an exact estimation value of the fatigue safe life; while the two-dimensional Weibull distribution method can get a range of values of fatigue safe lives, the fatigue safe lives of the specimens which after LSP were a range from 116570 to 150230, the average value was 132330. The two-dimensional Weibull distribution method has more engineering applicability and can be used to estimate the fatigue safe lives with fewer experiments.

Abstract: The heat-resistant steel after aluminized was treated by laser shock processing (LSP) with high power Nd:YAG laser, and then was tensile tested at 400°C. The effects of the high-temperature behavior after LSP were analyzed from residual stress and fracture organization. The results showed that the yield strength and tensile strength of heat-resistant steel after aluminized were improved obviously during the tensile testing at high temperature, and the High-temperature fatigue life of 00Cr12 with composite processing was enhanced vastly. Compared with the LSP, the High-temperature fatigue life of 00Cr12 heat-resistant steel by aluminizing and LSP had a larger increase.

Abstract: Co-based alloy coating was fabricated by powder feeding laser cladding on T10 tool steel. The microstructure and phase composition were investigated by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The results showed that the different solidification microstructures on the section, such as planar, cellular and dendrite formed from the interface to the surface. The main phase γ-Co and another phase Cr23C6 existed in the original coating, however, the main phase γ-Co was unchanged, and another phase was replaced by Cr7C3 accompanying with Co3C and Co4B precipitations after aging treatment.

Abstract: The strain-rate sensitivity of LY2 aluminum (Al) alloy subjected to laser shock processing (LSP) was investigated according to the fracture morphology at strain-rates ranging from 0.00001 s-1 to 0.1 s-1. The fracture morphology was observed by the scanning electron microscopy (SEM). Fracture morphology at different strain-rates suggested that LY2 Al alloy after LSP seemed to evolve towards a more ductile dimple fracture mode with increasing the strain-rates. The relations underlying the fracture morphology and strain-rate sensitivity were also addressed.

Abstract: The deformation process of plate material shocked by high-power short pulsed laser is one of the key problems for laser shock forming. In this paper, the finite element software ABAQUS is used to simulate the deformation process. A simple and novel optoelectronic measurement system is applied to measure the deformation process of aluminum sheet. The experiment and simulation results show that the load from the high-power short pulsed laser irradiation can be regard as transient pressure and the dynamic displacement law is damped oscillation.

Abstract: The expander lens can match the beam dimension between two cascade amplifiers, so the laser medium can be used effectively and the laser output energy can be improved greatly. Study on the functions of the expander lens in high energy Nd:Glass laser is presented. It is shown that the output energy increases by 30% with the expander lens. The simulation through using the optical software CodeV indicates that adjusting the expander lens can effectively compensate the laser thermal lens, make the focusing beam into the parallel beam, and avoid damaging the optical elements. In addition, adjusting the expander lens may compress the laser beam divergence and focus the laser spot, which is beneficial to form high power density and meet the requirements of laser shock processing.

Abstract: Laser-aided direct metal deposition (LADMD) technique was used to fabricate Co-285+WC coatings on 1018 mild steels. The effects of the processing parameters (laser power P, addition amount of WC, scanning speed V) on the microhardness of the deposited coatings was analyzed. Results indicate that the microhardness of the matrix and the Rockwell hardness of the deposited coatings increases with the addition of WC and the P/V value. The addition amount of WC has the most important effect on the two hardness values, followed by the scanning speed and the laser power. Results of the optimized specimen in this study indicate that the deposited coating is composed of undissolved WC, dendrites, eutectics and the coral structures. The wear mechanism of the deposited coating is a mixture of abrasive, adhesive and oxidation wear.